Safety lifting system for a mechanical excavator

ABSTRACT

The present invention provides a lifting system for an excavator, comprising a movable linkage (e.g. a chain), an actuator adapted to be coupled to the linkage for displacement of the linkage thereof, an abutment member configured to limit the displacement of the linkage and a retaining assembly arranged to releasably retain a hook attached to the linkage. The actuator is operable to reversibly displace the linkage between a first position in which the hook is free from the assembly and a second position in which the hook is retained by the assembly. As a result, the linkage may be safely stowed to avoid harm or injury to an operative associated with the lifting system.

The present invention relates to lifting systems, and particularly relates to a safety lifting system for a mechanical excavator.

Mechanical excavators, such as diggers, JCBs, mechanical shovels and 360-degree excavators, are commonly used on construction sites and throughout heavy industry, including mining and demolition. In general, such excavators typically share the same basic design, and thus usually comprise a boom arm that is controlled via a hydraulic piston or ram (invariably referred to as the “crowning ram”) which is most often fitted to the top of the boom arm via suitable brackets.

The crowning ram is usually connected to a pair of tipping links, which are themselves connected to a quick-hitch (i.e. latching device) that serves to lock a tool or attachment, for example a bucket, claw or drill, to the overall boom arm assembly. Each of these components are typically connected to each other via a series of pins.

The tool or attachment is therefore operated by controlled movement of the crowning ram and boom arm, enabling the tool or attachment to be positioned at the exact location at which the digging, lifting, or scraping operation etc. is to be carried out.

However, there are certain operations which are typically better performed without a tool or attachment being connected to the boom arm, and in such circumstances it is common for one or more linkages, such as metal chains etc., to be attached to the end of the boom arm in order to allow various types of objects to be lifted. One such example occurs when there is a need to lift paving components (e.g. paving slabs and/or edging) or objects such as wooden or concrete sleepers etc. In such cases, the chains are then attached to the objects (for example via a hook and harness), which enables the objects to be lifted and transported to a desired location via controlled operation of the crowning ram and boom arm.

However, a significant drawback of using such chains is that these may potentially cause harm or injury if they are allowed to dangle or freely hang during times when the excavator is not in use and when no attachment is connected to the boom arm. Consequently, operatives are typically required to remove the chains from the boom arm after the lifting operation is complete. Therefore, once the chains have been removed these must then usually be stowed away on the excavator itself (e.g. via in-built storage compartments) or otherwise be transported away to a safe storage location. Difficulty arises in this operation due to the weight of the chains, which are usually in excess of 25 kg and may sometimes even weigh more than 100 kg. The reverse operation of re-installing the chains may therefore be even more problematic for an operative, as the chains need to be supported while manually raising them up to the boom arm whereupon they are reconnected to the arm via a shackle.

Hence, not only is this operation potentially hazardous to an operative, but it may require the assistance of several operatives in order to be achieved, which is not only wasteful of time and resources, but may also expose more operatives to possible harm or injury. Moreover, the removal and re-installation of the chains may also need to take place during conditions of inclement weather, which may pose further risk to the operative(s) while also being generally unpleasant for all concerned.

Hence, it is an object of the present invention to address some, if not all, of the above problems in the art, by providing an attachable and/or permanent lifting system for an excavator that allows lifting operations to be carried out without harm or injury to an associated operative.

According to an aspect of the present invention there is provided a safety lifting system for an excavator, the system comprising:

a movable linkage;

an actuator adapted to be coupled to the linkage for displacement of the linkage thereof;

an abutment member configured to limit the displacement of the linkage; and

a retaining assembly arranged to releasably retain a hook attached to the linkage,

wherein the actuator is operable to reversibly displace the linkage between a first position in which the hook is free from the assembly and a second position in which the hook is retained by the assembly.

The provision of a lifting system comprising, at least, an actuator which is operable to reversibly displace a linkage between a first position in which a hook is free from the retaining assembly and a second position in which the hook is retained by the retaining assembly is found to be particularly advantageous over the prior art.

The functionality to reversibly move and latch/lock the hook in a second position thereby provides the capability to effectively ‘stow’ the linkage away or otherwise limit its movement/displacement relative to the boom arm of the excavator. As a result of this action, the linkage is then prevented from dangling or hanging freely from the boom arm, which not only avoids the need to remove and re-install the linkage between excavator operations but also importantly minimises the risk of harm or injury to an operative associated with the excavator as there is no danger of the linkage coming into unforeseen contact with the operative.

By ‘excavator’ we mean any mechanical excavator, whether that be mobile or static, and/or hydraulically, electrically and/or pneumatically powered, and is particularly intended to include the non-exhaustive list of diggers, JCBs, mechanical shovels and 360-degree excavators, without limitation.

Moreover, it is to be appreciated that any references herein to a ‘linkage’ is intended to include all forms of chain, cables, tethers and any other segmented mechanical couplings in the form of a chain, cable or tether, which incorporate a mechanical hook or hook-like component. Most preferably, the linkages associated with this invention will be heavy gauge metal chains.

The lifting system of the present invention may be retro-fitted to any existing type of excavator or alternatively may be installed during initial fabrication of the excavator. Where the lifting system is retro-fitted, the system may be scaled to suit or match the size and/or configuration of the physical dimensions of the particular boom arm and excavator itself. Therefore, it should be appreciated that the present system is inherently scalable and may be used in conjunction with most, if not all, models of excavator, subject to any modifications as prescribed herein.

The actuator is adapted to be coupled to the linkage, such as a chain, for displacement of the linkage. The actuator is preferably attached to the boom arm of the excavator, either permanently or detachably, via appropriate couplings, such as rigid brackets and pins etc.

In particularly preferred embodiments, the actuator is in the form of a hydraulic piston or ram that is operable to reversibly extend and retract under the action of hydraulic pressure. In other embodiments, the actuator may be electrically or pneumatically driven, or possibly driven via a combination of all three.

Where the actuator is a hydraulic piston or ram, the piston/ram may be coupled directly to the existing hydraulic system of the excavator. Moreover, the control system of the excavator (usually provided within the cabin or seated area of the excavator) may also be modified to incorporate a switching gear (e.g. switch, button, level, joystick etc.) to operably control the actuator via the existing control system. Therefore, in preferred embodiments an electrical switch may be used to activate the hydraulic system to thereby extend or retract the hydraulic ram.

Preferably, the lifting system further comprises an engaging member coupled to an end portion of the actuator, the engaging member being configured to engage with the abutment member when the hook is free from the retaining assembly, namely when the linkage has been displaced to the first position.

The engaging member is most preferably in the form of a piston ram block, that is connected or otherwise coupled to the extendible end of the hydraulic ram.

The piston ram block may comprise a solid body, preferably including coupling means to enable the linkage to be coupled to the actuator. The body may be shaped to include a neck portion of relatively smaller dimension to that of the remainder of the body. The neck portion being that part which is preferably connected to the hydraulic ram.

The coupling means may be in the form of a pair of projections, that preferably project along the direction of movement of the hydraulic ram. The function of the projections is to allow the chain to be coupled to the piston ram block via a suitable retaining means, such as a pin or a bolt etc., that preferably passes through a link of the chain and through the projections.

The abutment member is configured to limit the displacement of the linkage. In preferred embodiments, the abutment member is in the form of a piston block housing, which preferably comprises a bore to enable the linkage to pass therethrough. In alternative embodiments, the bore may be replaced by an open topped channel or recess etc.

The piston block housing may comprise a solid body having a substantially inverted ‘U-shape’ or horseshoe shape. However, any other suitable shape may be used depending on the particular application and/or implementation of the lifting system.

The piston block housing preferably comprises an abutment surface to inhibit movement of the piston ram block, which may be extended into and retracted from the piston block housing under the action of the actuator. The abutment surface may correspond to an internal wall or other surface of the piston block housing.

In preferred embodiments, the lifting system may further comprise at least one guide rail for guiding the displacement of the engaging member. Most preferably, the lifting system incorporates a pair of guide rails that extend along at least part of the boom arm of the excavator substantially co-axial with the direction of movement of the actuator.

Hence, in a particularly preferred embodiment, the guide rails extend from the abutment member along an upper surface of the boom arm, which permits the engaging member to be located and guided along the rails, thereby enabling reliable alignment of the engaging member with the abutment member during extension and retraction of the actuator.

The engaging member may comprise at least one laterally extending pin or lug adapted to engage with the guide rail. Most preferably, the engaging member will comprise a pair of pins, oppositely opposed on each side of the engaging member. The function of the pins is to ensure proper engagement and alignment with the rails, which themselves preferably comprise a respective recessed channel or groove to receive a pin. However, as will be appreciated, any suitable slot and pin arrangement may be used to guide the movement and alignment of the engaging member.

The guide rails may be covered via any suitable means to prevent debris and contaminants (e.g. dirt, stones, dust, mud etc.) from entering into the region substantially between the rails. The covering means of the guide rails may also include a plastic liner comprising downwardly-directed fibres, fingers or stipples etc., which are intended to reduce clattering or clunking of the linkage as it passes therethrough.

The retaining assembly is arranged to releasably retain the hook attached to the linkage. In particularly preferred embodiments, the retaining assembly comprises an automatic gripping mechanism for retaining the hook.

The gripping mechanism preferably comprises a pair of pivotable surfaces biased towards each other in order to grip the hook. In an exemplary embodiment, the pivotable surfaces are in the form of a pair of spring-loaded paddles that may be deflected and which automatically press against the hook to thereby releasably grip the hook therebetween.

The retaining member may be in the form of a substantially flat rectangular box through which the linkage is able to pass through one end and out the other. An aperture or opening at one end is dimensioned to allow a hook to enter into, and emerge from, the box. Preferably, the spring-loaded paddles are disposed adjacent to the opening to thereby releasably grip the hook when the hook enters the box.

The surfaces of the paddles that contact the hook may include a respective recess to facilitate easier gripping of the hook.

The retaining assembly preferably further comprises a hook ejection mechanism. The hook ejection mechanism may comprise a biased plate including an aperture to enable the linkage to pass therethrough. The biased plate is preferably spring-loaded, and most preferably comprises a pair of compressible springs.

When the actuator retracts the engaging member from the abutment member, the linkage is drawn through the retaining assembly until the hook is engaged with the paddles in the retaining assembly. The hook preferably presses against the biased plate, which due to the compressible springs provides an ejecting force to the hook when the actuator is again extended. In this way, the biased plate effectively provides a push or kick to the hook enabling the hook to be ejected from the retaining assembly. While the hook is retained, the linkage is thereby essentially stowed, or otherwise inhibited/prevented from moving, which avoids the linkage from dangling or hanging freely with respect to the boom arm. As a result, there is then little or no risk of the linkage coming into unforeseen contact with an operative associated with the excavator, while the act of stowing the linkage avoids the need to remove and re-install the linkage between use of the excavator.

It is to be appreciated that by ‘stow’ or ‘stowing’ we mean that the linkage is safely held against, adjacent to, or otherwise in relation to the boom arm of the excavator and as such remains out of harms way when the attachment to the excavator has been removed. Hence, when the linkage is stowed, the linkage is displaced to the second position, in which the hook is retained by the assembly, or conversely, when the hook is retained by the assembly, the linkage is then safely stowed away.

The retaining assembly may be covered by any suitable means to prevent debris and contaminants (e.g. dirt, stones, dust, mud etc.) from entering into the assembly. For box-like arrangements, the cover may correspond to a simple lid or cap etc.

In preferred embodiments, the aperture in the biased plate of the retaining assembly may have a tapered edge to receive a reciprocally shaped neck of the hook. This is to ensure that the hook fully engages with the plate, so that the ejection mechanism provides the maximum ejection force when the actuator is extended.

The use of a hook with a substantially conical shaped neck is most preferable, as not only will such a hook engage fully with the biased plate, but this will also ensure that the hook lies essentially flat when it enters the retaining assembly. Preferably, the conical shaped neck is truncated such that a flat surface is present adjacent to where the moveable linkage is connected to the hook. The flat surface advantageously may facilitate full engagement with the biased plate.

Preferably, the conical shaped neck is narrower adjacent the linkage than adjacent the hook. Advantageously, this facilitates guiding into place of the hook within the retaining assembly.

Preferably, the conical shaped neck is not circular in cross-section and has a greater extension in one dimension than the other. For example, the conical shaped neck may be elliptical in cross-section or may be Obround in cross-section.

The retaining assembly may also include a wear plate that serves as an inclined surface (e.g. ramp) for guiding the hook into the biased plate, while also facilitating ease of displacement of the linkage through the assembly. In addition, the wear plate may also reduce any noise associated with the linkage ‘clattering’ or ‘clunking’ through the biased plate and the assembly itself.

As mentioned previously, the lifting system of the present invention may be retro-fitted to an existing excavator or installed as part of the fabrication of a new excavator. In some cases, it may be necessary to modify the position and arrangement of the crowning ram. Hence, it is envisaged that for at least some types of excavator, the brackets of the crowning ram may need to be increased by around 10-15 mm or more to create space for the actuator. Moreover, it may also be the case that a recess or channel be cut or drilled in the upper surface of the boom arm, again to accommodate the axial movement of the actuator.

Where any structural changes are made to the boom arm, one or more strengthening plates may be fixed to the arm to provide additional support. However, in most case, this would not be necessary.

Further modifications may also include the need to relocate/re-position one or more hydraulic feed lines and/or the pipes associated with the quick-hitch. However, all of the modifications would be well within the capabilities of a skilled person in this field.

To prevent wear to the boom arm, and also reduce noise, plastic wear plates or shims may be fitted to the upper surface of the boom arm to avoid the linkage from rubbing or clattering against the arm. Therefore, a shim may be fitted between the abutment member and the retaining assembly.

In addition, a metal wear plate may be fixed to the end of the boom arm, which preferably has upturned edges to serve as a guide for the linkage and to prevent the linkage from entering into the gap where the quick-hitch is fixed to the boom arm.

As will be appreciated the lifting system as described in the foregoing embodiments advantageously has few moving parts and in exemplary embodiments the retaining assembly itself requires no electronics or hydraulics for operation. Therefore, the lifting system is not only reliable but is also easy to service and maintain—thereby promoting longevity of use.

Moreover, the whole system typically weights around 100 kg or less, which does not affect the performance of the excavator, nor does it hinder any of its capabilities in any way.

The present invention also provides an excavator comprising a lifting system according to any of the preceding embodiments.

It is to be understood that none of the embodiments described in relation to the present invention are mutually exclusive, and therefore the features and functionality of one embodiment may be used interchangeably or additionally with the features and functionality of any other embodiment without limitation.

Embodiments of the present invention will now be described in detail by way of example and with reference to the accompanying drawings in which:

FIG. 1—shows a side view of an example boom arm having associated therewith a particularly preferred embodiment of the present invention;

FIG. 2—shows a side close-up view of the embodiment of FIG. 1;

FIG. 3—shows a top plan view of a particularly preferred embodiment of a lifting system according to the present invention;

FIGS. 4a & 4 b—show respective top plan and side end views of an abutment member and engaging member according to a particularly preferred embodiment of the present invention;

FIG. 5—shows a top plan view of a retaining assembly according to a particularly preferred embodiment of the present invention; and

FIGS. 6a and 6b —show respective side and angled views of a hook and linkage according to a particularly preferred embodiment.

Referring to FIG. 1, there is shown a particularly preferred embodiment of a lifting system 10 according to the present invention. The lifting system 10 is shown attached to an example excavator 30 having a boom arm 31 and a hydraulic (crowning) ram 32 fitted on top of the boom arm 31 via brackets 33. The crowning ram 32 is connected to tipping links 34, which are in turn connected to a quick-hitch 35 that acts to secure the tool or attachment 36 (shown in ghost lining) to the boom arm 31, as conventionally known in the prior art.

The lifting system 10 comprises a movable linkage 14, an actuator 11 adapted to be coupled to the linkage 14, an abutment member 12 configured to limit the displacement of the linkage 14 and a retaining assembly 13 arranged to releasably retain a hook 15 attached to the linkage 14. The skilled person will appreciate that the term “hook” encompasses any suitable mechanism for connecting loads to the moveable linkage 14. Such suitable mechanisms may include open hooks, closed hooks (which may be referred to as an eyelet), or the like.

In the example of FIG. 1, the linkage is a metal chain 14 of heavy gauge. In other embodiments, the linkage may be other forms of flexible member.

The actuator 11 is in the form of a hydraulic piston or ram, that is operable to reversibly extend and retract under the action of hydraulic pressure. The hydraulic ram 11 is attached to the boom arm 31 of the excavator 30 via a rigid bracket and pin 16.

The hydraulic ram 11 is coupled directly to the existing hydraulic system 37 of the excavator 30. It is possible that some modification to the hydraulic feed lines/pipes may be required, depending on the particular implementation and/or type of excavator be used. However, the modification would not be onerous and would be well within the knowledge and expertise of the skilled person. Therefore, the lifting system of the present invention may be retro-fitted to most, if not all, excavators.

Moreover, the control system of the excavator 30 (usually provided within the cabin or seated area of the excavator—not shown in the figures) may also be modified to incorporate an appropriate switching gear (e.g. switch, button, level, joystick etc.) to operably control the hydraulic ram 11 via the existing control system. Again, such a modification would be a routine exercise for a skilled person.

Therefore, in practice an electrical switch (not shown) would be used to activate the hydraulic system 37 to thereby extend or retract the hydraulic ram 11.

Referring now to FIGS. 1 and 2, the lifting system 10 further comprises an engaging member 11 a coupled to an end portion of the hydraulic ram 11, the engaging member 11 a is configured to engage with the abutment member 12 when the hook 15 is free from the retaining assembly 13, namely when the chain 14 has been displaced to the first position (as described in further detail below).

The engaging member 11 a is in the form of a piston ram block, that is welded to the extendible end of the hydraulic ram 11.

The piston ram block 11 a comprises a solid body including coupling means 11 b to enable the chain 14 to be coupled to the hydraulic ram 11. As best shown in FIGS. 3 and 4 a, the body is shaped to include a neck portion of relatively smaller dimension to that of the remainder of the body. The neck portion being that part which is welded to the hydraulic ram 11, as shown in FIG. 3.

Referring to FIG. 4a , the coupling means 11 b are in the form of a pair of projections, that project along the direction of movement of the hydraulic ram 11 (cf. FIG. 3). The function of the projections is to allow the chain 14 to be coupled to the piston ram block 11 a via a suitable retaining means, such as a pin or a bolt etc., that passes through a link of the chain 14 and through the projections.

The abutment member 12 is configured to limit the displacement of the chain 14 and is in the form of a piston block housing. The piston block housing 12 comprises a bore to enable the chain 14 to pass therethrough (cf. FIGS. 2, 3 and 4 a).

As shown in FIGS. 3 and 4 a, the piston block housing 12 comprises a solid body having a substantially inverted ‘U-shape’ or horseshoe shape. The solid body is fabricated from heavy cast steel and would be welded to the upper surface of the boom arm 31, as shown in FIGS. 1 and 2.

The piston block housing 12 comprises an abutment surface 12 a (as shown in FIG. 4a ) to inhibit movement of the piston ram block 11 a, which may be extended into and retracted from the piston block housing 12 under the action of the hydraulic ram 11 (cf. FIGS. 3 and 4 a). The abutment surface 12 a corresponds to an internal wall of the piston block housing 12 and may be created via the casting process or else later machined after the body has been cast.

The lifting system 10 further comprises a pair of guide rails 17 that extend along at least part of the boom arm 31 of the excavator 30 substantially co-axial with the direction of movement of the hydraulic ram 11 (see FIGS. 3 and 4 a).

The guide rails 17 extend from the piston block housing 12 along the upper surface of the boom arm 31, which permits the piston ram block 11 a to be located and guided along the rails 17, as shown in FIG. 3. In this way, a reliable alignment of the piston ram block 11 a with the piston block housing 12 can be achieved during extension and retraction of the hydraulic ram 11.

Referring to FIGS. 4a and 4b , the piston ram block 11 a comprises a pair of pins or lugs 11 c (shown in ghost lining), oppositely opposed on each side of the piston ram block 11 a. The function of the pins 11 c is to ensure proper engagement and alignment with the rails 17, which themselves comprise a respective recessed channel or groove to receive a pin 11 c (see ghost lining in FIG. 4b ).

Although not shown in FIGS. 3 and 4 a, the guide rails 17 may be covered by a removable access cover, such as made from a metal sheet (e.g. light steel), that is screwed or bolted onto the rails 17 to thereby avoid any debris and contaminants (e.g. dirt, stones, dust, mud etc.) from entering into the region between the rails. The covering means of the guide rails 17 may also include a plastic liner comprising downwardly-directed fibres, fingers or stipples etc., which are intended to reduce clattering or clunking of the chain 14 as it passes therethrough.

The retaining assembly 13 is arranged to releasably retain the hook 15 attached to the chain 14 via an automatic gripping mechanism.

Referring to FIGS. 3 and 5, the gripping mechanism comprises a pair of pivotable surfaces 13 a biased towards each other in order to grip the hook 15. The pivotable surfaces 13 a are in the form of a pair of spring-loaded paddles that may be deflected and which automatically press against the hook 15 to thereby releasably grip the hook therebetween.

The retaining member 13 is in the form of a substantially flat rectangular box through which the chain 14 is able to pass through one end and out the other (cf. FIG. 3). The box is made from steel plate, typically 4-12 mm in thickness. An aperture or opening 13 b at one end is dimensioned to allow the hook 15 to enter into, and emerge from, the box. The spring-loaded paddles 13 a are disposed adjacent to the opening 13 b to thereby releasably grip the hook 15 when the hook enters the box, under the action of compressible springs 13 c.

The surfaces of the paddles 13 a that contact the hook 15 may include a respective recess to facilitate easier gripping of the hook. The paddles 13 a would be made from tempered steel.

The retaining assembly 13 further comprises a hook ejection mechanism. The hook ejection mechanism includes a biased plate 13 d including an aperture to enable the chain 14 to pass therethrough (cf. FIG. 3). The biased plate 13 d is spring-loaded and comprises a pair of compressible springs 13 e.

During use, when the hydraulic ram 11 retracts the piston ram block 11 a from the piston block housing 12, the chain 14 is drawn through the retaining assembly 13 until the hook 15 is engaged with the paddles 13 a in the retaining assembly 13 (cf. FIG. 3). The hook 15 then presses against the biased plate 13 d, which due to the compressible springs 13 e provides an ejecting force to the hook 15 when the hydraulic ram 11 is again extended.

In this way, the biased plate 13 d effectively provides a push or kick to the hook 15 enabling the hook to be ejected from the retaining assembly 13. While the hook 15 is retained, the chain 14 is thereby essentially stowed, or otherwise inhibited/prevented from moving, which avoids the chain 14 from dangling or hanging freely with respect to the boom arm 31. As a result, there is then little or no risk of the chain 14 coming into unforeseen contact with an operative associated with the excavator 30, while the act of stowing the chain 14 avoids the need to remove and re-install the chain between use of the excavator 30.

Although not shown for the purposes of clarity, the retaining assembly 13 may be covered by a removable lid, cover or cap to prevent debris and contaminants (e.g. dirt, stones, dust, mud etc.) from entering into the mechanism of the assembly.

The aperture in the biased plate 13 d of the retaining assembly 13 may have a tapered edge (not shown) to receive a reciprocally shaped neck of the hook 15. This is to ensure that the hook 15 fully engages with the plate 13 d, so that the ejection mechanism provides the maximum ejection force when the hydraulic ram 11 is extended.

The use of a hook 15 with a substantially conical shaped neck 50 is most preferable, as not only will such a hook engage fully with the biased plate 13 d, but this will also ensure that the hook lies essentially flat when it enters the retaining assembly 13 (cf. FIG. 3).

As shown in FIGS. 6a and 6b , the conical shaped neck 50 may be truncated such that it has a flat surface 52 at an end region adjacent the linkage 14. Conveniently, the hook 15 has flat faces 53 which help to ensure that the hook lies essentially flat within the retaining assembly. In the embodiment being described, the conical shaped neck 50 has a cross section which is sometimes referred to as “obround”; a cross-section consisting of two semicircles connected by parallel lines tangent to their endpoints.

As shown in FIG. 5, the retaining assembly 13 also includes a wear plate 13 f that serves as an inclined surface (e.g. ramp) for guiding the hook 15 into the biased plate 13 d, while also facilitating ease of displacement of the chain 14 through the assembly 13. In addition, the wear plate 13 f may also reduce any noise associated with the chain ‘clattering’ or ‘clunking’ through the biased plate 13 d and the assembly itself.

The conical shaped neck 50 may be narrower adjacent the linkage 14 than adjacent the hook 15.

The linkage 14 may be pivotably connected to the hook 15 by means of a bar, bolt, pin or the like 54 through the conical shaped neck 50 of the hook 15.

As mentioned previously, the lifting system 10 of the present invention may be retro-fitted to an existing excavator 30 or installed as part of the fabrication of a new excavator. In some cases, it may be necessary to modify the position and arrangement of the crowning ram 32. Hence, it is envisaged that for at least some types of excavator, the brackets 33 of the crowning ram may need to be increased by around 10-15 mm or more to create space for the hydraulic ram 11. Moreover, it may also be the case that a recess or channel of around 10-15 mm be cut or drilled and welded in the upper surface of the boom arm 31, again to accommodate the axial movement of the hydraulic ram 11.

Where any structural changes are made to the boom arm 31, one or more metal strengthening plates (not shown) of around 5-6 mm in thickness may be fixed to the arm to provide additional support. However, in most case, this would not be necessary.

Further modifications may also include the need to relocate/re-position one or more hydraulic feed lines and/or the pipes associated with the quick-hitch 35. However, all of the modifications would be well within the capabilities of a skilled person in this field.

To prevent wear to the boom arm 31, and also reduce noise, plastic wear plates or shims (not shown) may be fitted to the surface of the boom arm 31 to avoid the chain 14 from rubbing or clattering against the arm. Therefore, a shim may be fitted between the piston block housing 12 and the retaining assembly 13. The thickness of the shims would be around 5 mm.

In addition, a metal wear plate (not shown) may be fixed to the end of the boom arm 31, which has upturned edges to serve as a guide for the chain 14 and to prevent the chain from entering into the gap where the quick-hitch 35 is fixed to the boom arm 31. Again, the wear plate would be around 5 mm in thickness, with the upturned edges being about 20 mm in height.

As will be appreciated from the foregoing embodiments, the present invention provides a reliable and safe lifting system for an excavator that is scalable and easy to install. However, it should be recognised that one or more of the principles of the invention may also extend to other lifting systems, both mobile and static and irrespective of size, where there is a risk that a linkage or similar component may cause harm or injury to an operative associated with the system.

The above embodiments are described by way of example only. Many variations are possible without departing from the invention. 

1. A lifting system for an excavator, the system comprising: a movable linkage; an actuator adapted to be coupled to the linkage for displacement of the linkage thereof; an abutment member configured to limit the displacement of the linkage; and a retaining assembly arranged to releasably retain a hook attached to the linkage, wherein the actuator is operable to reversibly displace the linkage between a first position in which the hook is free from the assembly and a second position in which the hook is retained by the assembly.
 2. The lifting system of claim 1, wherein the retaining assembly comprises an automatic gripping mechanism for retaining the hook.
 3. The lifting system of claim 2, wherein the gripping mechanism comprises a pair of pivotable surfaces biased towards each other in order to grip the hook.
 4. The lifting system of claim 3, wherein the pivotable surfaces are in the form of a pair of spring-loaded paddles.
 5. The lifting system of claim 2, wherein the retaining assembly further comprises a hook ejection mechanism.
 6. The lifting system of claim 5, wherein the hook ejection mechanism comprises a biased plate including an aperture to enable the linkage to pass therethrough.
 7. The lifting system of claim 6, wherein the biased plate is spring-loaded.
 8. The lifting system of claim 6, wherein the aperture has a tapered edge to receive a reciprocally shaped neck of the hook.
 9. The lifting system of claim 1, wherein the abutment member is in the form of a piston block housing.
 10. The lifting system of claim 9, wherein the piston block housing comprises a bore to enable the linkage to pass therethrough.
 11. The lifting system of claim 1, further comprising an engaging member coupled to an end portion of the actuator, the engaging member being configured to engage with the abutment member when the hook is free from the assembly.
 12. The lifting system of claim 11, wherein the engaging member is in the form of a piston ram block.
 13. The lifting system of claim 12, wherein the abutment member comprises an abutment surface to inhibit movement of the piston ram block.
 14. The lifting system of claim 11, further comprising at least one guide rail for guiding the displacement of the engaging member.
 15. The lifting system of claim 14, wherein the engaging member comprises at least one laterally extending pin adapted to engage with the guide rail.
 16. The lifting system of claim 1, wherein the actuator is a hydraulic ram.
 17. An excavator comprising a lifting system according to claim
 1. 